Conventionally, ellipsometry (polarization analysis technology) is known as technology for investigating the optical characteristic, more generally, the dielectric characteristic of a substance. In ellipsometry, change of a polarization state is measured in case incident light reflects from a substance. The dielectric characteristic of a substance can be known from the change of the polarization state. The change of the polarization state is measured as a ratio of amplitude reflection coefficients rp and rs for p- and s-polarization, respectively. The amplitude reflection coefficients rp and rs are complex numbers, and the ratio, namely, the amplitude reflection coefficient ratio ρ=rp/rs, is also a complex number and expressed using two ellipsometric angles ψ and Δ as ρ=tan(ψ) exp(iΔ). The ellipsometric angles ψ and Δ, acquired as a measurement result, are dependent on the optical characteristic of each substance and the thickness of reflective film, etc. The ellipsometry device and the ellipsometry method by the ellipsometry are used in order to measure film characteristic and thickness of a thin film in the semiconductor field processing a thin film of thickness below the light wavelength, etc.
The ellipsometry device for thin film measurement is called an ellipsometer. An ellipsometer is used in order to obtain the optical constants, film thickness, layer structure, etc. of a thin film by measuring change of the polarization state in the light reflected from the thin film. The conventional ellipsometer is classified roughly into a type of device which rotates a polarizer mechanically, and a type of device which modulates light polarization using photoelasticity. There are two for the polarizer rotation: one rotates analyzer (polarizer); and the other rotates a compensator. The change of the polarization state, generated when an incident light changes into a reflected light, is measured by a setup of the polarization state of the incident light and a detection of the polarization state of the reflected light.
Measurement is done by measuring the light intensity of the reflected light, during rotating the polarizer mechanically or modulating the light by transmitting the light through a photoelastic modulator, in order to measure under different conditions or an optimal condition. Operation of the mechanical rotation of the polarizer or the light phase modulation, for the setup of the polarization state or for the detection, lengthens the measuring time. Then, an ellipsometer, which improves measurement speed by removing the actuator rotating the polarizer, has been proposed (for example, refer to patent document 1).
The accuracy of thin film measurement can be improved by using the information on a wavelength other than the amplitude reflection coefficient ratio ρ. In this case, not only the measurement of film thickness or optical constants of a single layer film, structural analysis of a multilayer film can be made. A spectroscopic ellipsometer is one of the ellipsometers which use wavelength information. The spectroscopic ellipsometer uses combination of the polarization analysis technology (ellipsometry) and the spectrum analysis technology (spectroscopy). For the measurement, a high-performance spectroscope is necessary in addition to the polarization devices such as a rotary polarizer, a rotary compensator or a photoelastic modulator, and thus the ellipsometer becomes expensive.
Also, as one of the technologies for analyzing light waves such as reflected light, there is a holography, which analyzes the light by recording the light intensity data and light wave phase data together on a medium such as a photographic plate called a hologram. Recent holography analyzes the hologram by recording the light intensity and phase of the light wave as digital data using an image sensor and a semiconductor memory, or by generating the hologram on a computer. Such holography is called digital holography.
In the digital holography, various technology have been proposed to achieve high-speed recording and high precision processing of holograms. For example, in order to record and analyze a complex amplitude in-line hologram at a high speed and accurately, a one-shot digital holography, in which spatial frequency filtering and spatial heterodyne modulation are applied to a recorded hologram, has been proposed (for example, refer to patent document 2). In order to solve the problem of the conventional optical microscope, a method for precisely recording one-shot object light of large numerical aperture without using an imaging lens, a method for precisely reconstructing a high resolution three-dimensional image with a computer reconstruction by performing plane wave expansion of the recorded object light, and, a lensless three-dimensional microscope capable of recording and reconstructing a distortionless high-resolution three-dimensional moving image have been proposed (for example, refer to patent document 3).
Moreover, in order to measure internal structures of cells in a culture solution and/or biological tissues with high resolution, a high resolution tomographic imaging method using a reflection type lensless holographic microscope and wavelength swept laser lights has been proposed (for example, refer to patent document 4). Furthermore, a method for synthesizing an object light of a numerical aperture exceeding 1 by combining a plurality of large numerical aperture object lights recorded with illumination lights of different incident angles, and an ultrahigh resolution three-dimensional microscope of resolution exceeding the diffraction limit (for example, refer to patent document 5).
Also, in relation to the digital holography, a dispersive Fourier transform spectroscopy (DFTS) is known, which obtains optical constants of a measurement sample, by making a beam transmitted through a measurement sample interfere with a beam not transmitted, receiving the beams by a CCD, and Fourier-transforming the interference image (for example, refer to non-patent document 1). Similarly, a method for measuring the thickness of a thin film sample using interference spectroscopy is known, which derives the thickness by Fourier-transforming an interference image of a beam transmitted through the measurement sample and a beam not transmitted and calculating an light path length (for example, refer to non-patent document 2). Further, an interference contrast film-thickness-measurement method is known, which derives the thickness of a thin film sample by illuminating the measurement sample with a parallel light generated using a hologram, dividing the light transmitted through the measurement sample, making them interfere mutually after generating phase change, and measuring the intensity change of the interference fringe (for example, refer to patent document 6).